1.There are five pairs____,but I'm at loss which to choose.

1.There are five pairs____,but I'm at loss which to choose.
A to be chosen
B to choose from
C to choose
D for choosing
2.After she considered the problem,she got a tall box to stand_____.
A by
B on
C up
D with
3.Charles Babbage is generally considered______the first computer.
A to invent
B inventing
C to have invented
D having invented
4.'Where is Davied?""He is upstairs____ready to go out."
A to get
B getting
C to be getting
D having got
5.With a lot of difficult problems_____,the newly-elected president is having a hard time.
A settled
B setting
C to be settled
D being settled
6.If the car won't start,____it.
A try push
B try pushing
C try to push
D to try pushing